The present invention is directed to conversion between heat and electricity. More particularly, the invention provides systems and methods for recovery of waste heat. Merely by way of example, the invention has been applied to a modular thermoelectric unit that can be easily assembled and scaled up to an optimal sized system for providing solutions for various heat recovery applications including industrial combustion processes with enhanced power output, reduced parasitic power losses, and lowered manufacture cost. However, it would be recognized that the invention has a much broader range of applicability.
Any process that consumes energy usually is not 100% efficient and often generates waste energy, usually in the form of heat. For example, the industrial combustion process generates a substantial amount of waste heat via an exhaust gas flow at high temperature. In order to improve the efficiency of the combustion process, effectively capturing and converting some of this waste heat into a useful form without disturbing the primary operation would be desired. A conventional technique that has been considered is to place thermoelectric (TE) devices onto the exhaust system associated with the combustion process.
The thermoelectric devices are made from thermoelectric materials that can convert an appreciable amount of thermal energy into electricity in an applied temperature gradient (e.g., the Seebeck effect) or pump heat in an applied electric field (e.g., the Peltier effect). Interest in the use of thermoelectric devices that comprise thermoelectric materials has grown in recent years partly due to the heightened need for systems that recover waste heat as electricity to improve energy efficiency in the industrial combustion process.
To date, thermoelectrics have had limited commercial applicability often due to poor cost effectiveness and low conversion performance in comparison with other technologies that accomplish similar energy generation or refrigeration. Where there are almost no other technologies as suitable as thermoelectrics for lightweight and low footprint applications, thermoelectrics have nonetheless been limited by their high costs in thermoelectric materials and the manufacture of high-performance thermoelectric devices. The thermoelectric materials in conventional thermoelectric modules are generally comprised of bismuth telluride or lead telluride, which are toxic, difficult to manufacture with, and expensive to procure and process.
More recently, advances in developing and manufacturing nano-structured materials with enhanced thermoelectric performance have been initiated. In particular, the thermoelectric performance of the nano-structured material is characterized by, e.g., high efficiency, high power density, or high “thermoelectric figure of merit” ZT (where ZT is equal to S2σ/k, and S is the Seebeck coefficient, σ is the electrical conductivity, and k is the thermal conductivity). This technical development drives a need for devices and/or systems in both alternative energy production and microelectronics that usually requires high manufacturability and low cost. This technical development also drives the need for converting waste heat in exhaust from many industrial systems, such as industrial combustion process, into useful electrical power.
FIG. 1 is a simplified diagram showing a conventional heat recovery system using one or more thermoelectric device components for generating power from a waste heat source. As shown, in a conventional heat recovery system 4000 (e.g., a conventional thermoelectric generation system), one or more thermoelectric (TE) device components 4010 are attached on one side to a hot plate 4020 of a hot-side heat exchanger 4022 and leave the other side subjecting to one or more cold fluid flows 4030 (e.g., one or more cold air flows, one or more cold gas flows). As shown, the one or more thermoelectric device components 4010 are disposed entirely outside the main hot flow region 4040. The hot plate 4020 is thermally connected to an extended conductor 4024 with multiple fins 4026 sticking into the hot flow region 4040. For example, one or more hot fluid flows 4042 (e.g., one or more hot air flows, one or more hot gas flows) move out of an exhaust pipe or a chimney 4044, and the extended conductor 4024 and the multiple fins 4026 serve as an indirect thermal energy collector. But such indirect thermal energy collector often is quite inefficient in utilizing the one or more hot fluid flows 4042 of the waste heat.
To take advantage of the high-temperature thermoelectric devices and flexibly apply these devices for various industrial combustion processes without disturbing the operation of the primary process, it is highly desirable to make an improved thermoelectric system for enhanced power output, lowered parasitic power loss, and reduced cost.